Um... hi,
This is pretty random but for a piece of writing I'm working on I'm going to need a character in a coma for about 2-6 weeks and have forgotten most events around 6 months before the incident (less time can be adjustable).
From my research, coma caused by near-drowning or by head injury would probably be best for this amount of time as it can depend how serious the injuries were etc.
I'm planning on my patient to recover well with nothing that will really affect anything except the loss of memory, but I really just cannot find any information that would tell me what kind of after-effects there would be and what kind of impact that would have on the patient. I'm not even entirely sure if these symptoms are existent, to be honest
I'd really appreciate it if anyone knew and could tell me how this could be worked into the story (preferably, it should have been caused by another person).

I'm sorry if this is in the wrong place.
My character is 16 years old, if it makes a difference.
Thank you for any help,
- Imma Simma

Look up the long term effects of a brain injury - I had loads of hits in Google actually. Seeing as it varies on an individual basis, and which part of the brain that was injured, it's quite a complex subject, and you'd be able to pick and choose from a wide array of lasting side effects - difficulty speaking or understanding language, spatial impairment etc.

Memory loss after a coma is usually due to the injury itself, not the coma, so you'd want to figure out what kind of head injury the character has. Could be oxygen deprivation after a near-drowning, or a hit to the head, or a stroke (aneurism, or another type of hemorrhagic stroke). A traumatic event in itself can also cause amnesia.

Near-drowning is more likely to cause widespread brain damage. A hit to the head in just the right place is probably more likely to cause memory loss.

There are also several types of memory loss.
Some are unable to remember the events that caused the accident (or some weeks or months before the accident), and this is called post-traumatic amnesia. Some can't remember anything at all, or perhaps only their childhood but not that they're married and have kids, which is retrograde amnesia. Others can be unable to form new memories from the point where they are (only remembering things prior to the accident), and any new memories will not last. This is called anterograde amnesia. There are more types in the link.

Oh, and don't do the whole going from deep coma to wide awake in a minute. That's not how waking from a coma happens in real life. If the coma is lengthy (weeks to months) it usually takes a while for the patient to wake up, and they usually wake up in stages. How long it takes varies, but it's rarely coma to wide awake and fully functioning in just a few minutes, like you see in a lot of TV series and films that don't really know what they're doing.

Wikipedia is my way of doing quick research. The English Wiki is actually quite good and detailed on medical themes. It's nice for browsing through various things if you need to know something very quick, or as a starting point for further research, but it's not 100% trustworthy, so don't trust it blindly. Going to other sources as well is a good idea, once you know what you want to know more about. There may also be books with personal experiences, as well as blogs. These can be very useful for research, as you don't only get the medical side but the personal experience.

Some search words: Coma, amnesia, traumatic brain injury, Glasgow Coma Scale, head/brain trauma, hypoxia (or just click on the blue words in the coma article on Wiki).

Depending on how deep you want to dive into the theme, there's lots of stuff to find. If you need inspiration through TV series (such as medical jargon or ideas for scene setups), then ER (although slightly outdated), Grey's anatomy (the medical bits, not the kiss-kiss-bang-bang), Saving Hope, and House are the ones most rooted in truth, medical-wise. They're a bit over the top like most other TV series, but they have actual medical advisors, so they mostly know what they're doing. Most other TV series or films featuring comatose patients or medical stuff rarely know what they're doing...

I'm currently writing a sims-story (and slowly doing a complete rewrite, for a book project) where one of the characters does end up in a coma, so I can tell you, the research you can do on this theme is pretty much endless. I've only skimmed the surface of it, and I've dipped into a lot of the stuff having to do with brain injuries and such, just to get an overview. My character had a hemorrhagic stroke and some other problems, and not amnesia (but other problems related to brain injury), but there are several similarities, so I did a bit of reading on traumatic brain injury as well. I've got some real-life experience with stroke patients (as a nursing student), so I'm more comfortable with that particular theme.

You'll have to do the main research yourself (that's the only way you'll be able to use it in your writing - having people tell you something isn't the same as doing research for yourself), but if you need any pointers, or have any questions, feel free to ask.

I think with head injuries you are pretty much free to make it up as you go along, the reason being that injuries to the brain and their consequences are as individual as the people who have them. You might think that sounds callous but I'm actually quoting the surgeon who did my brain surgery after I gave him a long list of symptoms in the months after my surgery that I thought he should know about. He used to shrug and say something like 'well, yes, that could be due to the tumour and/or surgery. Or, then again, it might not.' I guess that doesn't help much but don't worry about being inaccurate anyway. Remember, the brain controls more or less everything about us and an injury, depending on where it is and what happened during that injury event, means that the effects of that injury can be just about anything.

I think the choice of a head injury is probably a good one (or drowning). Head injuries, of course, can be catastrophic (and I'd be the last person you'd ever meet to under-estimate the effect of that) but people get lucky and do recover. The recent example in the news of Michael Schumacher (recent good news is that he is apparently coming out of his coma which was partly medically induced anyway) is an example of that. Or at least, we hope it is (fingers crossed for him).

Anyway, as I said, I had a brain tumour - so not the same as a head injury, except that my surgeon said (he said a lot of things) that surgery is just the same as an injury in reality - and I can try to answer any questions you have if you want to ask. My experience is that after-effects generally fall into three categories (and this is dependent on where the injury is and what the situation was): 1. physical; 2. mental and 3. emotional and psychological. To give you some idea of what I'm talking about I'll give you some examples from my experience. However, you should remember that people have very different experiences with this.

Examples
1. physical problems might result from injury to a part of the brain that controls movement. In my case, my tumour was in the cerebellum and close to my ears. This means that after surgery I have problems with my sense of balance and have a tendency to fall over or nearly fall over in certain situations (downward travelling escalators are a nightmare and I avoid using them). I manage it and most of the time it's not a big problem. That's very common with post-injury people, you learn to live with it by learning what to do and what to avoid though adapting can be frustrating.

2. mental problems are usually things like memory or processing information. Memory problems are very common. In my case, I have big gaps in my memory and if people ask me things about the period when I was illest, I often just can't remember. When I was first recovering, this gave me some real problems and caused distress. I would meet people who obviously knew me and I simply couldn't remember them - at all - no amount of brain-beating could drag up memories. It could be very embarrassing. It's become much less of an issue as time passed but at first that was hard.

3. Emotional/psychological problems - this, I guess, is obvious and it has to be said that a major illness or injury certainly brings changes to the person, almost, in some cases, leading to significant shifts in personality. In my case, I would say (or at least am told), I am essentially the same person but there have been some big shifts and changes in my emotional outlook. You shouldn't make the assumption though that those things are all negative. People who haven't experienced major trauma often get very upset with people like me because they assume that we must be emotionally charged and grief-stricken. It would be a mistake to say that you don't grieve for what you've lost but many people I have met (myself included) would not go back and change what happened. We often see it, in the long run anyway, as something that brought about a much happier state of mind. That kind of thing makes you realise what's important. And what's important is the love of your family and friends and the quality of your life. You get rid of the crap and end up not caring much what other people think. I can recommend it as a way to live.

Which brings me on to say, please don't feel embarrassed or awkward if you want to ask questions. I am not upset about what happened (it's 15 years ago now anyway) and, believe me, you couldn't possibly ask me anything that is worse than what I went through anyway.

I guess that's possibly a bit more extreme than you had in mind but perhaps it'll give you some ideas.

Thanks so much for all the responses, it's been really helpful.
And I'm sorry to hear about your brain tumor, Maxon.